The present invention relates to a nozzle seal slot tool and method and, more particularly, to a nozzle seal slot tool including a continuous measurement pin capable of providing continuous measurement data and having a readable scale.
It is desirable to control the position of seal slots within drawing dimensions because the seals fit within the slots of adjacent nozzle segments. If the seal slot positions are not aligned between adjacent segments, it will not be possible to install the seals. Service run nozzles in a gas turbine may have distorted sidewalls as a result of previous weld repairs or due to stress relief during service. Creep strain due to applied loads at operating temperatures may also contribute to distortion. This movement of the sidewalls will cause the seal slots that are contained within the sidewalls to be out of position relative to engine center.
The operator needs to know how far out of position the slots are to press the walls, and therefore slots, back into position. If the sidewalls are not pressed back into position, the seal slots between adjacent segments would not be aligned with each other, and it may prove impossible to fit the seals in place. Alternatively, it may be possible to force the seals into the slots but this would lock the nozzle segments together such that they could not move or “float” relative to each other. This float is necessary to allow for thermal expansion and to ensure the segments load up against the sealing faces (hook fit and chordal hinge) during operation. If they are locked together, it is likely they will be skewed and will not load against their sealing faces. This will result in compressor discharge air leaking directly into the hot gas path and will reduce the amount of air available for combustion and for cooling of the nozzle. The result of reduced air for combustion will be lower performance of the turbine and increased emissions. A reduction in available cooling air will result in increased oxidation of the nozzle due to a resultant higher metal temperature and the lack of cooling will also cause changes to thermal gradients within the nozzle leading to increased cracking of the part. This will increase subsequent repair costs and may reduce the life of the parts.
Misaligned sidewalls may also result in flow path steps. The hot gas will not have a smooth path but will be tripped by the mismatch between adjacent nozzle segments, resulting in turbulent flow and reduced energy of the gas stream, thereby reducing engine performance. Turbulent flow also increases thermal transfer to the nozzle and so will raise the metal temperature, leading to increased oxidation and cracking.
Seal slot position measurement is currently conducted by means of a “go/no-go” gauge, typically having two flats mounted on a precision ground shaft. To perform the measurement, a pedestal assembly is positioned adjacent the turbine. The pedestal assembly includes a series of bushings that are precisely positioned for slot measurement. The gauge is inserted into the seal slots via the bushings to determine whether the opening is smaller or larger than a fixed amount, which is defined by the tool. The gauge thus only allows for crude measurement within set limits.